There are two types of portable terminals with the communication function: one is a portable terminal that uses a single CPU, and the other is a portable terminal that uses multiple CPUs, for managing and controlling the communication function and the other service functions (for example, see Patent Document 1).
As the service function of a portable terminal is extended and sophisticated, more and more portable terminals will use multiple CPUs.
One CPU is a communication control CPU (CCPU) that controls and manages the RF (radio frequency) unit and the signal processing DSP (digital signal processor) required primarily for the actual communication. The other CPU is an application control CPU (ACPU) that controls and manages the user interface for the liquid crystal display unit, the audio input/output unit, the key unit, and the optical unit of the portable terminal.
Today, more and more portable terminals use multiple CPUs. This is because a single-CPU portable terminal, if used for managing and controlling both the communication function that does not functionally change so much and the application function such as the digital camera function or the game function that is extended and added, requires a long time and a high cost for developing the CPU and its control software. The single-CPU configuration also involves a high possibility of design errors and therefore causes the increases of the development risk.
In the multiple-CPU configuration, the ACPU and the CCPU are controlled as follows. When data processing is not performed, the ACPU is usually placed in the sleep state to consume less power; when data communication is not performed, the CCPU is usually placed in the sleep state to consume less power except when it monitors a communication start request sent from an external unit. For example, when communication is requested through the user key operation that is the user interface, the ACPU starts the CCPU to allow the CCPU to carry out communication.
However, in the intermittent reception operation mode in which the communication is turned on and off at a regular interval to monitor the call acceptance state, the CCPU enters the active state and sleep state in synchronization with the time at which the intermittent reception operation is executed. However, the ACPU cannot sense this time. If the ACPU sends a transmission request to the CCPU randomly, the CCPU in the sleep state is forced to start and, as a result, the consumption current flows. This consumption current shortens the operation time, the call time, and the wait time of the portable terminal driven by a battery. Therefore, there is a need for a CPU operation method for minimizing the waste.
[Patent Document 1] Japanese Patent Kokai Publication No. JP-A-11-85337